Isozymes, speciation and evolution in the polyploid complex Cochlearia L. (Brassicaceae)

Within the genus Cochlearia L. sect. Cochlearia three isozyme systems (aspartate aminotransferase, leucine aminopeptidase and phosphoglucomutase) have been analysed at the populational level for eleven species with different ploidy levels. Nine loci complexes were resolved with a total of 33 alleles from 89 populations. In general, polyploids displayed higher numbers of alleles per species and per population. A notable exception is diploid C. pyrenaica with as many alleles as some polyploids. Data support: (1) the origin of tetraploid C. officinalis from C. pyrenaica s.l., particularly from C.aestuaria; (2) the atuopolyploid origin of octoploid C. anglica from C. officinalis; (3) the allopolyploid origin of hexaploid inland taxa C. polonica, C. tatrae and C. bavarica via hybridization between C. pyrenaica and C. officinalis; (4) a putative allopolyploid origin of hexaploid coastal species C. danica by hybridization between C. pyrenaica s.l. and C. officinalis accompanied by a shift in chromosome complement. A scenario summarizing our present understanding of the evolution within Cochlearia sect. Cochlearia is presented.